The present invention discloses a method of safely disposing of used drilling mud and reclaiming hydrocarbons separated therefrom. The drilling of oil and gas wells involves the use of various different compositions of drilling fluid or mud. The drilling mud is heavier than water and is employed to increase the hydrostatic head in the wellbore and to provide a suitable medium for circulating the material removed by the drill bit to the surface of the earth.
Oil based mud is sometime used as the drilling fluid. While forming a borehole into the earth, various hydrocarbon bearing formations are penetrated by the drill bit and this also accounts for hydrocarbon becoming admixed with the drilling mud. Accordingly, the used drilling mud contains hydrocarbons, weight increasing compounds such as barite, the removed formation that forms the borehole, various salts, and many other objectionable compounds which must be properly disposed of so that they do not enter and contaminate our environment, especially flowing streams and the underlying aquifer.
There are many salt domes or salt formations located below the surface of the earth. These salt formations can be penetrated by a wellbore and water circulated into the salt formation, thereby leaching the salt and forming a cavity, also called a salt cavern or a salt jug. The water dissolves the salt and becomes salt water, also called 10 pound brine. The brine can be sold to drilling companies so that it can be admixed with drilling mud and used as a component of drilling fluid.
In certain geographical areas of the United States, such as West Texas, there is an underground geological formation referred to as the Rustler formation. In the Rustler formation, the salt formations were formed by nature in a more or less sandwiched relationship with respect to a number of smaller anhydride formations. When a borehole is sunk into a salt formation contained in the Rustler formation, the salt can be solubilized with water to form a solution cavity, leaving vertically spaced layers of anhydride formations remaining within the cavity due to the anhydride being insoluble in brine. The anhydride formations are relatively flat, thin, horizontally extending formations spaced apart from one another and are often formed throughout the salt formation. Accordingly, a large salt cavity having a capacity of millions of barrels can be formed within a salt formation, with the cavity being intersected by a plurality of anhydride ledges that have been arranged by nature in a more or less vertically spaced, horizontal planes. The insoluble anhydride ledges therefore interrupt the solution cavity and form a baffle-like structure therewithin which provide unexpected and desirable results respective to the present invention.